(a) Field of the Invention
The present invention relates to a high-speed all-band-cell search cellular phone and a method for searching the band cell based on the specification of IMT-2000 (International Mobile Telecommunications-2000) prescribed in the specification of 3GPP (3rd Generation Partnership Project) standard.
(b) Description of the Related Art
In general, a cellular phone (or mobile station) uses a band-cell search technique for detecting the band cell of the own station for telecommunication. FIG. 8 shows the band-cell detection block of a cellular phone for detecting the band cell. The band-cell detection block 20 includes a RSSI (received signal strength indicator) measurement circuit 22 for measuring the received power levels of a 5-MHz-wide band of the RF signal, a cell search circuit 23 for performing an ordinary cell search for a desired a frequency, and a waiting cell determination circuit 24 for determining the waiting cell based on the information of a tentative waiting cell delivered from the RSSI measurement circuit 22 and the cell search circuit 23. Both the RSSI measurement circuit 22 and the cell search circuit 23 receive the radio frequency (RF) signal through a receiver 21, which receives the RF signal through an antenna (ANT) 24, and deliver signals of the tentative waiting cell to the waiting cell determination circuit 24.
In the cellular phone, a so-called all-band-cell search technique is generally used for detecting the base station to which the location of the cellular phone is to be registered, either after the initial power-on of a cellular phone after it is first introduced into the cellular phone system or after a long-time absence of the cellular phone in the service area. The long-time absence may occur, for example, if the cellular phone travels a long distance while it is turned off and thus there exits no clue for the location identification of the own station. The waiting cell determination circuit 24 receives signals of the tentative waiting cell from the RSSI measurement circuit 22 and cell search circuit 23, and sets the waiting cell after communication with the base station by using the tentative waiting cell.
In the specifications of IMT-2000 prescribed in 3GPP standard, assuming that the RF signal in a cellular phone system uses a total bandwidth of 60 MHz between 2110 MHz and 2170 MHz and that the space between the central frequencies of adjacent two channels is 200 KHz, the number of frequency channels or carriers amounts to 300. All these carriers may be referred to as FID1 to FID300 based on the central frequencies thereof.
The all-band-cell search process includes the steps of slot synchronization to slot identification by the cell search circuit 23 and the step of measuring the received signal code power by the RSSI measurement circuit 22 for each of 5-MHz-wide bands of whole the 60-MHz-wide band to select a 5-MHz-wide band. Thus, the all-band-cell search consumes a large amount of processing time in the cellular phone. For example, if a band-cell search consumes 100 milliseconds for each channel and the band cell of the own station exists only in the FID300 carrier, the all-band-cell search consumes 30 seconds in total after the power-on or long-time absence, assuming that the search is conducted in the ascending order of FIDs in the cellular phone.